Localized heating via an infrared heat source array of edge seals for a vacuum insulating glass unit, and/or unitized oven with infrared heat source array for accomplishing the same

ABSTRACT

Certain example embodiments of this invention relate to edge sealing techniques for vacuum insulating glass (VIG) units. More particularly, certain example embodiments relate to techniques for providing localized heating to edge seals of units, and/or unitized ovens for accomplishing the same. In certain example embodiments, a unit is pre-heated to one or more intermediate temperatures, localized heating via at least one substantially two-dimensional array of heat sources is provided proximate to the peripheral edges of the unit so as to melt frits placed thereon, and cooled. In certain non-limiting implementations, the pre-heating and/or cooling may be provided in one or more steps. An oven for accomplishing the same may include multiple zones for performing the above-noted steps, each zone optionally including one or more chambers. Accordingly, in certain example embodiments, a temperature gradient proximate to the edges of the unit is created, thereby reducing the chances of breakage and/or at least some de-tempering of the substrates.

This application is a continuation of application Ser. No. 14/975,908,filed Dec. 21, 2015 (U.S. Pat. No. 9,783,447), which is a continuationof application Ser. No. 13/942,734, filed Jul. 16, 2013 (now U.S. Pat.No. 9,221,707), which is a continuation of application Ser. No.12/000,791, filed Dec. 17, 2007 (now U.S. Pat. No. 8,506,738), theentire disclosures of which are all hereby incorporated herein byreference in this application.

FIELD OF THE INVENTION

Certain example embodiments of this invention relate to edge sealingtechniques for vacuum insulating glass (VIG) units. More particularly,certain example embodiments relate to techniques for providing localizedheating to edge seals of units, and/or unitized ovens for accomplishingthe same. In certain example embodiments, a unit is pre-heated to one ormore intermediate temperature(s), localized heating via at least onesubstantially two-dimensional array of heat sources is providedproximate to the peripheral edges of the unit so as to melt frit(s)placed thereon, and the unit is cooled. In certain exampleimplementations, the pre-heating and/or cooling may be provided in oneor more steps. An oven for accomplishing the same may include multiplezones for performing the above-noted steps, each zone optionallyincluding one or more chambers.

BACKGROUND AND SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

Vacuum IG units are known in the art. For example, see U.S. Pat. Nos.5,664,395, 5,657,607, and 5,902,652, the disclosures of which are allhereby incorporated herein by reference.

FIGS. 1-2 illustrate a conventional vacuum IG unit (vacuum IG unit orVIG unit). Vacuum IG unit 1 includes two spaced apart glass substrates 2and 3, which enclose an evacuated or low pressure space 6 therebetween.Glass sheets/substrates 2 and 3 are interconnected by peripheral or edgeseal of fused solder glass 4 and an array of support pillars or spacers5.

Pump out tube 8 is hermetically sealed by solder glass 9 to an apertureor hole 10 which passes from an interior surface of glass sheet 2 to thebottom of recess 11 in the exterior face of sheet 2. A vacuum isattached to pump out tube 8 so that the interior cavity betweensubstrates 2 and 3 can be evacuated to create a low pressure area orspace 6. After evacuation, tube 8 is melted to seal the vacuum. Recess11 retains sealed tube 8. Optionally, a chemical getter 12 may beincluded within recess 13.

Conventional vacuum IG units, with their fused solder glass peripheralseals 4, have been manufactured as follows. Glass frit in a solution(ultimately to form solder glass edge seal 4) is initially depositedaround the periphery of substrate 2. The other substrate 3 is broughtdown over top of substrate 2 so as to sandwich spacers 5 and the glassfrit/solution therebetween. The entire assembly including sheets 2, 3,the spacers, and the seal material is then heated to a temperature ofapproximately 500° C., at which point the glass frit melts, wets thesurfaces of the glass sheets 2, 3, and ultimately forms hermeticperipheral or edge seal 4. This approximately 500° C. temperature ismaintained for from about one to eight hours. After formation of theperipheral/edge seal 4 and the seal around tube 8, the assembly iscooled to room temperature. It is noted that column 2 of U.S. Pat. No.5,664,395 states that a conventional vacuum IG processing temperature isapproximately 500° C. for one hour. Inventor Collins of the '395 patentstates in “Thermal Outgassing of Vacuum Glazing,” by Lenzen, Turner andCollins, that “the edge seal process is currently quite slow: typicallythe temperature of the sample is increased at 200° C. per hour, and heldfor one hour at a constant value ranging from 430° C. and 530° C.depending on the solder glass composition.” After formation of edge seal4, a vacuum is drawn via the tube to form low pressure space 6.

Unfortunately, the aforesaid high temperatures and long heating times ofthe entire assembly utilized in the formulation of edge seal 4 areundesirable, especially when it is desired to use a heat strengthened ortempered glass substrate(s) 2, 3 in the vacuum IG unit. As shown inFIGS. 3-4, tempered glass loses temper strength upon exposure to hightemperatures as a function of heating time. Moreover, such highprocessing temperatures may adversely affect certain low-E coating(s)that may be applied to one or both of the glass substrates in certaininstances.

FIG. 3 is a graph illustrating how fully thermally tempered plate glassloses original temper upon exposure to different temperatures fordifferent periods of time, where the original center tension stress is3,200 MU per inch. The x-axis in FIG. 3 is exponentially representativeof time in hours (from 1 to 1,000 hours), while the y-axis is indicativeof the percentage of original temper strength remaining after heatexposure. FIG. 4 is a graph similar to FIG. 3, except that the x-axis inFIG. 4 extends from zero to one hour exponentially.

Seven different curves are illustrated in FIG. 3, each indicative of adifferent temperature exposure in degrees Fahrenheit (° F.). Thedifferent curves/lines are 400° F. (across the top of the FIG. 3 graph),500° F., 600° F., 700° F., 800° F., 900° F., and 950° F. (the bottomcurve of the FIG. 3 graph). A temperature of 900° F. is equivalent toapproximately 482° C., which is within the range utilized for formingthe aforesaid conventional solder glass peripheral seal 4 in FIGS. 1-2.Thus, attention is drawn to the 900° F. curve in FIG. 3, labeled byreference number 18. As shown, only 20% of the original temper strengthremains after one hour at this temperature (900° F. or 482° C.). Such asignificant loss (i.e., 80% loss) of temper strength is of courseundesirable.

In FIGS. 3-4, it is noted that much better temper strength remains in athermally tempered sheet when it is heated to a temperature of 800° F.(about 428° C.) for one hour as opposed to 900° F. for one hour. Such aglass sheet retains about 70% of its original temper strength after onehour at 800° F., which is significantly better than the less than 20%when at 900° F. for the same period of time.

Another advantage associated with not heating up the entire unit for toolong is that lower temperature pillar materials may then be used. Thismay or may not be desirable in some instances.

Even when non-tempered glass substrates are used, the high temperaturesapplied to the entire VIG assembly may melt the glass or introducestresses. These stresses may increase the likelihood of deformation ofthe glass and/or breakage.

Thus, it will be appreciated that there is a need in the art for avacuum IG unit, and corresponding method of making the same, where astructurally sound hermetic edge seal may be provided between opposingglass sheets. There also exists a need in the art for a vacuum IG unitincluding tempered glass sheets, wherein the peripheral seal is formedsuch that the glass sheets retain more of their original temper strengththan with a conventional vacuum IG manufacturing technique where theentire unit is heated in order to form a solder glass edge seal.

An aspect of certain example embodiments of this invention relates toapplying localized heating to the periphery of a unit to form edge sealsto reduce the heating of the non-peripheral areas of the unit andthereby reduce the chances of the substrates breaking.

An aspect of certain example embodiments relates to providing stagedheating, localized heating, and staged cooling of a unit via a unitizedoven, the localized heating being provided by a substantially linearfocused infrared (IR) heat source comprising an array or matrix oflinear heat sources.

Another aspect of certain example embodiments relates to providing avacuum IG unit having a peripheral or edge seal formed so that at leastcertain portion(s) of thermally tempered glass substrates/sheets of thevacuum IG unit retain more of their original temper strength than ifconventional edge seal forming techniques were used with the solderglass edge seal material.

Another aspect of certain example embodiments relates to providing avacuum IG unit, and method of making the same, wherein at least aportion of the resulting thermally tempered glass substrate(s) retain(s)at least about 50% of original temper strength after formation of theedge seal (e.g., solder glass edge seal).

Another aspect of certain example embodiments relates to reducing theamount of post-tempering heating time necessary to form aperipheral/edge seal in a vacuum IG unit.

In certain example embodiments of this invention, there is provided amethod of making a vacuum insulating glass (VIG) window unit, the methodcomprising: providing first and second substantially parallelspaced-apart glass substrates and a frit provided at least partiallybetween the first and second glass substrates for sealing an edge of theVIG window unit; pre-heating the glass substrates and the frit to atleast one temperature below a melting point of the first and secondsubstrates and below a melting point of the frit; providing localizednear infrared (IR) inclusive heat via at least one substantiallytwo-dimensional array of heat sources proximate to the edge to be sealedso as to at least partially melt the frit; and cooling the unit andallowing the frit to harden in making the vacuum insulating glass (VIG)window unit.

In certain example embodiments of this invention, a method of making avacuum insulating glass unit including an edge seal thereof is provided.There is provided a unit comprising first and second substantiallyparallel spaced-apart glass substrates, one or more edges between thefirst and second substrates to be sealed, and a frit for sealing eachsaid edge to be sealed. The unit is pre-heated in its entirety to atleast one intermediate temperature, each said intermediate temperaturebeing below a melting point of the first and second substrates and belowa melting point of the frit. Via near infrared radiation generated viaat least one substantially two-dimensional array of heat sources,localized heat is provided to the unit proximate to the edges to besealed at a frit melting temperature, the frit melting temperature beingsufficiently high to melt the frit, the localized heat being provided tothe unit such that areas of the unit not proximate to the edges to besealed are maintained at a temperature close to an intermediatetemperature. The unit is cooled in its entirety to at least one reducedtemperature and the frit is allowed to harden.

In certain example embodiments, a method of making an edge seal for avacuum insulating glass unit is provided. An oven including entrance,edge sealing, and exit zones is provided. A unit comprising first andsecond substantially parallel spaced-apart glass substrates, one or moreedges between the first and second substrates to be sealed, and a fritfor sealing each said edge to be sealed is inserted into the oven. Inthe entrance zone of the oven, the unit is pre-heated in its entirety toat least one intermediate temperature, each said intermediatetemperature being below a melting point of the first and secondsubstrates and below a melting point of the frit. In the edge sealingzone of the oven, there is provided, via a localized heat sourcecomprising at least one substantially two-dimensional array of heatsources, localized heat to the unit proximate to the edges to be sealedat a frit melting temperature, the frit melting temperature beingsufficiently high enough to melt the frit, the localized heat beingprovided to the unit such that areas of the unit not proximate to theedges to be sealed are maintained at a temperature close to anintermediate temperature. In the exit zone of the oven, the unit iscooled in its entirety to at least one reduced temperature and the fritis allowed to harden.

In certain example embodiments, an apparatus for forming edge seals forvacuum insulating glass units is provided. An entrance zone is providedfor receiving a unit comprising first and second substantially parallelspaced-apart glass substrates, one or more edges between the first andsecond substrates to be sealed, and a frit for sealing each said edge tobe sealed, and for pre-heating the unit in its entirety to at least oneintermediate temperature, each said intermediate temperature being belowa melting point of the first and second substrates and below a meltingpoint of the frit. An edge sealing zone including a localized heatsource comprising at least one substantially two-dimensional array ofheat sources is provided for providing localized heat to the unitproximate to the edges to be sealed at a frit melting temperature, thefrit melting temperature being sufficiently high enough to melt thefrit, the localized heat being provided to the unit such that areas ofthe unit not proximate to the edges to be sealed are maintained at atemperature close to an intermediate temperature. An exit zone of theoven is provided for cooling the unit in its entirety to at least onereduced temperature and allowing the frit to harden.

In certain example implementations, the heat sources in the array arearranged in a plurality of rows and columns, and the rows and/or columnsare staggered in certain example implementations. In certain exampleimplementations, each heat source in each row and column of the arraymay be selectively activated in dependence on whether an edge to besealed is proximate to the heat source.

The features, aspects, advantages, and example embodiments describedherein may be combined to realize yet further embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages may be better and morecompletely understood by reference to the following detailed descriptionof exemplary illustrative embodiments in conjunction with the drawings,of which:

FIG. 1 is a prior art cross-sectional view of a conventional vacuum IGunit;

FIG. 2 is a prior art top plan view of the bottom substrate, edge seal,and spacers of the FIG. 1 vacuum IG unit taken along the section lineillustrated in FIG. 1;

FIG. 3 is a graph correlating time (hours) versus percent temperingstrength remaining, illustrating the loss of original temper strengthfor a thermally tempered sheet of glass after exposure to differenttemperatures for different periods of time;

FIG. 4 is a graph correlating time versus percent tempering strengthremaining similar to that of FIG. 3, except that a smaller time periodis provided on the x-axis;

FIG. 5 is a simplified side view illustrating an example layout of afive chamber oven in accordance with an example embodiment;

FIG. 6 is an overhead view of the moving concentration of IR heatsources in the edge sealing zone of a unitized oven in accordance withan example embodiment;

FIG. 7 is a side view of a concentration and/or focusing mirror locatedproximate to an IR heating element in accordance with an exampleembodiment;

FIG. 8 is an illustrative flowchart showing a process for providinglocalized heating to frit edge seals of a VIG assembly via a unitizedoven, in accordance with an example embodiment; and

FIG. 9a is an overhead view of the VIG assembly on a belt in an ovenprior to its entry under the IR source array, in accordance with anexample embodiment;

FIG. 9b is an overhead view of the VIG assembly on a belt in an ovenentering into the IR source array, in accordance with an exampleembodiment;

FIG. 9c is an overhead view of the VIG assembly further entering the IRsource array such that both the edge to be sealed along the minor axisof the VIG assembly and portions of the edges to be sealed along themajor axis of the VIG assembly are both exposed to IR from the IR sourcearray, in accordance with an example embodiment;

FIG. 9d is an overview of the VIG assembly further entering the IRsource array such that only the edges to be sealed along the major axisof the VIG assembly are exposed to IR from the IR source array, inaccordance with an example embodiment;

FIG. 9e is an overhead view of the VIG assembly exiting the IR sourcearray, in accordance with an example embodiment;

FIG. 9f is an overhead view of a second VIG assembly entering the IRsource array as a first VIG assembly exits the IR source array inaccordance with an example embodiment;

FIG. 10 is an overhead view of an IR source array incorporating astaggered IR heat source design, in accordance with an exampleembodiment;

FIG. 11a is a side view of an in-line style belt furnace installed withan array of IR sources in accordance with an example embodiment; and

FIG. 11b is a side view of an in-line style belt furnace installed withtwo arrays of IR sources in accordance with an example embodiment.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Certain embodiments of this invention relate to an improved peripheralor edge seal in a vacuum IG window unit, and/or a method of making thesame. “Peripheral” and “edge” seals herein do not mean that the sealsare located at the absolute periphery or edge of the unit, but insteadmean that the seal is at least partially located at or near (e.g.,within about two inches) an edge of at least one substrate of the unit.Likewise, “edge” as used herein is not limited to the absolute edge of aglass substrate but also may include an area at or near (e.g., withinabout two inches) of an absolute edge of the substrate(s). Also, it willbe appreciated that as used herein the term “VIG assembly” refers to anintermediate product prior to the VIG's edges being sealed andevacuation of the recess including, for example, two parallel-spacedapart substrates and a frit. Also, while the frit may be said to be “on”or “supported” by one or more of the substrates herein, this does notmean that the frit must directly contact the substrate(s). In otherwords, the word “on” covers both directly and indirectly on, so that thefrit may be considered “on” a substrate even if other material (e.g., acoating and/or thin film) is provided between the substrate and thefrit.

In certain example embodiments of this invention, a method ofpreferential heating for frit edge seal of vacuum insulated glass unitsusing a unitized zoned oven is provided. The pre-assembled unit is firstheated to an intermediate temperature lower than that required to meltthe frit seal (e.g., a temperature of about 200-300° C.). Then, the edgeof the unit is further heated with localized heat from a substantiallylinear focused infrared (IR) heat source and/or via at least onesubstantially two-dimensional array of heat sources that is configuredto generate IR radiation at a near infrared wavelength (e.g., awavelength of about 0.7-5.0 μm) and, more preferably, of about 1.1-1.4μm, in order to provide a localized temperature of from about 350-500°C. until the frit is melted. At the same time, if tempered or heatstrengthened glass is used, at least certain portions of a thermallytempered glass sheet(s)/substrate(s) of the VIG unit lose no more thanabout 50% of original temper strength, as the majority of the area isstill under the intermediate temperature. Because of the overall lowertemperature, the techniques of certain example embodimentsadvantageously consume less energy and save time when the samples cooldown. It will be appreciated that the localized temperature may bedetermined based in part on the material(s) comprising the frit. Forexample, lead-inclusive frits tend to require lower temperatures thansilver-inclusive frits.

The unitized oven of certain example embodiments includes multiplechambers. Generally, the chambers will correspond to an entrance zone,an edge sealing zone, and an exit zone. It will be appreciated that anillustrative unitized oven may include multiple chambers foraccomplishing the functionality of a single zone (e.g., two entrancechambers may be provided for performing entrance zone functionality, twoexit chambers may be providing for performing exit zone functionality,etc.), and/or that a single chamber may be provided to accomplish thefunctionality associated with multiple zones (for example, a singlechamber may provide entrance and exit zone functionality, etc.).

By way of example and without limitation, FIG. 5 is a simplified sideview illustrating an example layout of a five chamber oven 50 inaccordance with an example embodiment. However, as alluded to above, itwill be appreciated that more or fewer chambers may be employed. Incertain non-limiting implementations, adjacent chambers may be separatedby sealing doors (represented by dashed lines in between adjacentchambers) located between them. Linkage, pulleys, and/or other means maybe provided to open and close such doors.

The unitized oven 50 of certain example embodiments is semi-continuousin terms of product flow. A roller conveyer 52 or other transporttechnique may be used to physically move a given VIG assembly from onezone and/or chamber to the next so that the VIG assembly and/or itscontents are not disturbed or repositioned relative to one another. At astart point 52 a, the roller conveyer 52 feeds VIG assemblies into theoven 50, e.g., through a first door 54. VIG assemblies may be moved intoplace and stopped when they reach a proper position within a chamberand/or zone. The position of the VIG assembly may be determined, forexample, by photo-eye or other detection means. By way of example andwithout limitation, the position may be the center of a particularchamber, aligned within particular horizontal and vertical positions(e.g., as described in greater detail below in relation to FIG. 6), etc.In certain example embodiments, it may be advantageous to temporarilystop a VIG assembly at a particular location, for example, to allow theVIG assembly to heat sufficiently, to allow a solder frit to melt, etc.

In certain example embodiments, multiple VIG assemblies may be fed intothe oven 50 at the same time so that they are processed in batch. Forexample, in a five-chamber oven like the one shown in FIG. 5, up to fiveVIG assemblies may be processed by the oven at a time, with the processbeing started and stopped in dependence on the progress of each chamber.For example, the edge sealing zone may require more time than thecooling performed in the exit zone chambers. Thus, there may be somedelay built into the process to account for the different process timesof the different zones and/or chambers.

The entrance zone (e.g., chambers 1 and 2 in the FIG. 5 exampleembodiment) is equipped with substantially uniform heat sources so thatthe VIG assembly is heatable in stages. That is, substantially uniformheat may be applied to the VIG assembly so as to substantially uniformlyheat the entire VIG assembly. Heating may be accomplished via IRradiation from an IR heat source or other means so as to reducedisturbance of the VIG assembly or its contents.

In an edge sealing zone (e.g., chamber 3 of FIG. 5), substantiallyuniform heating sources are installed to maintain the VIG assembly as awhole at a predetermined background temperature. This may beaccomplished by maintaining the entire VIG assembly at the intermediatetemperature from the entrance zone and/or slightly increasing thetemperature from the entrance zone. In the meantime, substantiallylinear focused IR heat sources 56 supply localized heating to theperimeter of the VIG assembly so as to melt the ceramic frit applied tothe edges. IR heat may be focused on peripheral edges, for example, bymeans of a parabolic mirror on an edge opposite to the VIG assembly.Further details of an example focusing mechanism are provided below withreference to FIG. 7. Although this particular zone is termed an edgesealing zone, it will be appreciated that some edge sealing may occur inother zones. For example, most melting will occur within the edgesealing zone and some edge sealing will take place once the IR radiationsources are powered down, although the edges may continue to seal (e.g.,the frit may begin or continue to harden) while in the exit zone.

FIG. 6 is an overhead view of the moving concentration of IR heatsources 62 and 64 in the edge sealing zone of a unitized oven inaccordance with an example embodiment. As shown in FIG. 6, the fritmelting oven is designed such that variously sized VIG assemblies may besealed. In certain example embodiments, one corner of the focused IRbank is fixed in position (e.g., the corner proximate to banks 62 a-b).In the FIG. 6 example, banks 62 a-b are fixed in position. In suchexample arrangements, only two sides of the focused IR bank would needto be repositioned to ensure proper frit melting. The IR sources alsomay be segmented into sections so that a part or all of the sections canbe turned on at any time to adjust the length of heating to that of theVIG assembly size. Parts of these IR source banks 64 a-b may be movedinto various positions around the perimeter of the VIG assembly bymechanical means, such as, for example, arms, rollers on a rail, and/orother linkages. In FIG. 6, this is shown as banks 64 a-b being segmentedand bank segments 64 a′-b′ being moved from their initial positions(designated by the dotted lines in the banks 64 a-b) to positionsproximate to the VIG assembly 1′ (designated by the solid lines) to beedge sealed. In the FIG. 6 embodiment, only IR sources corresponding tobanks 64 a′-b′ and parts of 62 a-b would be turned on; the rest of theIR sources in banks 64 a-b and the non-proximate IR sources in banks 62a-b need not be turned on (e.g., they would may remain off).

Thus, as is shown in FIG. 6, the localized heat source comprises first,second, third, and fourth banks of infrared heat source elements, thebanks being arranged such that the infrared heat source is substantiallyrectangularly shaped within the edge melting zone. The first and secondbanks are fixed in position and constitute two substantiallyperpendicular legs of the substantially rectangularly shaped infraredheat source, and the third and fourth banks constitute the other twosubstantially perpendicular legs of the substantially rectangularlyshaped infrared heat source. The infrared heat source elements of thesecond and third banks are movable in dependence on a size of the unitso as to move closer to the edges to be sealed.

In addition, the angle of the focusing mirror may be adjustable incertain example embodiments to allow the heat to be focused moreprecisely on the VIG assembly perimeters (as described in greater detailbelow with reference to FIG. 7). In certain example embodiments, the IRsegmented source movement and/or focusing may be computer-controlled toadjust the results of the individual units. Still further, the VIGassembly 1′ to be edge sealed may be elevated such that it is moreproximate to the IR sources. This may be accomplished by moving it intoa proper X-Y position with respect to the IR banks 62 a-b, movingportions of the movable IR banks 64 a-b, and lifting the VIG assembly 1′into position.

By way of example and without limitation, the IR sources within thebanks may be IR tubes. The IR tubes may be close enough to each toprovide heating across the edges of the VIG assembly (e.g., withoutleaving “gaps,” or unheated or substantially differently heated areasaround the edges), but also may be far enough away from each other toallow for movement of such tubes. Thus, by way of example and withoutlimitation, the IR tubes may be located approximately 5 mm apart incertain example embodiments. The sizes of the banks may vary independence on the needs of the VIG unit manufacturing process. Also byway of example and without limitation, banks of about 2-3 meters shouldaccommodate most standard VIG unit manufacturing requirements.

Referring once again to FIG. 5, the VIG assembly may be cooled down inan exit zone comprising one or more chambers, e.g., in a stepwise mannervia chambers 4 and 5 of FIG. 5. When a stepwise exit zone arrangement isimplemented, each successive exit zone chamber may be maintained at alower temperature than the previous exit zone chamber. This arrangementmay be enabled by using forced convective air cooling, cooling waterpiping, and/or other cooling means suitable for removing heat from theparticular exit zone chamber. Ultimately, the VIG assembly may be rolledout of the oven 50 through exit door 58 via rollers 52 b.

FIG. 7 is a side view of a concentration and/or focusing mirror 72located proximate to an IR heating element 74 in accordance with anexample embodiment. It will be appreciated that any type ofconcentrating and/or focusing mechanism may be used in connection withcertain other example embodiments. IR radiation from IR heating element74 is focused and/or concentrated by the parabolic mirror 72 onto orproximate to solder frit 4. The mirror 72 may be moved and/orrepositioned to cause more or less of the peripheral edges of the VIGassembly 1′ to be heated, to focus IR radiation to or away from thesubstrates 2 and 3, etc.

A more detailed description of the VIG assembly edge sealing processwill now be provided. A pre-assembled VIG assembly, which may include apre-applied and fired perimeter frit ink, enters the oven. In theentrance zone, the VIG assembly is heated up to a predeterminedtemperature of between about 200-300° C. This may be accomplished usingstaged heating in one or more entrance chambers, so that the entire VIGassembly is pre-heated to one or more intermediate temperatures. Ingeneral, the VIG assembly will enter into the oven at room temperature(e.g., which typically is about 23° C., although it will be appreciatedthat other processing environments and/or conditions may implement adifferent “room temperature”). The entire VIG assembly may be heated toabout 75° C. in a first entrance zone chamber and then to about 150° C.in a second entrance zone chamber. It will be appreciated that thepre-heating temperatures may vary by about ±50° C.

In the edge sealing zone, the entire VIG assembly is heated to about200° C., and an IR heat source (e.g., a computer-controlledsubstantially linear IR heat source) is moved into position and focusedaround the perimeter of the VIG assembly. The IR heat source isactivated at a predetermined distance (e.g., from about 0.5-10 cm) fromthe edge of the VIG assembly, depending in part on thefocusing/concentrating mirror, whether the IR radiation is meant to“contact” the top and/or bottom substrates or just the sides proximateto the frit, etc. As noted above, the IR heat source is focused, e.g.,by means of a parabolic mirror provided on a side of the IR heat sourceopposite to the VIG assembly. The temperature of the frit on theperimeter of the VIG assembly is controlled to about 350-500° C., whichis suitable to melt the frit but still below the melting point of theglass substrates, which varies from about 600-800° C. based on thecomposition of the glass. During the localized heating process in theedge sealing zone, the glass temperature remains at the backgroundtemperature. Accordingly, heat strengthened or tempered glass, ifutilized, is not de-tempered or suffers a reduced amount of de-temperingduring the frit heating and/or melting processes.

Following the frit melting in the edge sealing zone, the VIG assembly istransported to the exit zone. The exit zone may include one or moretemperature ramp-down areas (or chambers). The temperature is reduced sothat the VIG assembly is at a temperature less than about 100° C. whenit exits the oven. In certain example embodiments, in a first exitchamber, the temperature of the entire VIG assembly will be reduced toabout 150° C. and then to about 75° C. in a second exit chamber. Asabove, ramp-down temperatures may vary from these figures by as much asabout ±50° C.

FIG. 8 is an illustrative flowchart showing a process for providinglocalized heating to frit edge seals of a VIG assembly via a unitizedoven, in accordance with an example embodiment. In step S82, a VIGassembly including a plurality of edges to be sealed is inserted into aunitized oven. A roller conveyer may convey the VIG assembly into theoven, e.g., through a door. In step S84, the VIG assembly is pre-heatedto one or more intermediate temperatures in an entrance zone of theunitized oven. The intermediate temperature(s) is/are below the meltingpoints of glass and the frit along the edge to be sealed.

Localized heat is provided to the edges of the VIG assembly to be sealed(e.g., using one or more substantially linear IR heat sources, producingIR radiation having a near infrared wavelength (e.g., a wavelength ofabout 0.7-5.0 μm) and, more preferably, of about 1.1-1.4 μm) in an edgesealing zone of the unitized oven in step S86. The localized heat is ata temperature above the intermediate temperature(s) and is sufficient tocause the frit around the edges to melt. The temperatures may be chosenin dependence on the composition of the frit material. The VIG assembly,apart from the areas proximate to the peripheral edges to be sealed, arekept at a temperature close to that of the intermediate temperature(e.g., at a temperature sufficiently low so as to avoid melting of theglass, not varying by more than about ±50° C. from an intermediatetemperature).

In a step not shown, to provide localized heating, a plurality of heatsources (e.g., substantially linear IR heat sources) are provided, e.g.,within a bank. At least some of the banks may be fixed in position. TheVIG assembly may be positioned proximate to the fixed banks so that atleast some of the edges to be sealed are adjacent to the fixed banks.Additional banks including movable heat sources may be positioned so asto provide heat proximate to the edges of the VIG assembly that are notadjacent to the fixed banks. The areas to be heated may be more finelytuned by providing a concentration and/or focusing mirror.

Referring once again to FIG. 8, in step S88, the VIG assembly is cooledin an exit zone of the oven. The pre-heating and/or cooling of the VIGassembly may be staged so as to reduce the chances of breakage of theVIG assembly and/or de-tempering of the substrates comprising the VIGassembly. In certain example embodiments, multiple chambers may beprovided for one or more of the zones. In connection with suchembodiments, multiple chambers may be provided for the ramping-up oftemperatures and/or the cooling processes, e.g., when the heating and/orcooling processes are staged. In certain other embodiments, a singlechamber may be configured to perform the functionality of multiple zones(e.g., a single chamber may pre-heat and/or cool the substrate, a singlechamber may pre-heat the substrate and/or provide localized heat to theedges, a single chamber may provide localized heat to the edges and/orcool the substrate, etc.).

Thus, certain example embodiments advantageously heat, melt, and coolthe frit quickly. This helps produce a temperature gradient proximate tothe edges of the VIG assembly. The temperature gradient, in turn, helpsreduce de-tempering and/or the chances of breakage of the glass. Incertain example embodiments, at least certain portions of a thermallytempered glass sheet(s)/substrate(s) of the VIG unit lose no more thanabout 50% of original temper strength.

Certain example embodiments provide heat to the edges of the VIG using alocalized heat comprising an array of focused IR heat sources so thatwhile the non-edge areas remain at relatively low temperature, the fritaround the perimeter is melted. The array of IR heat sources reduces thenumber of moving parts in the localized heating source and does notnecessarily require separation between temperature zones someembodiments. The array is installable into a standard belt furnacerelatively easily. Another advantage of this design is that it can beused to produce VIG units of various sizes and shapes (e.g.,substantially rectangular and substantially non-rectangular shaped VIGunits of varying sizes).

Instead of, or in addition to, implementing system of movable heatsources, certain example embodiments may provide localized heating by asubstantially stationary array of focused IR sources installed anin-line furnace, such as belt furnace or “coffin” style furnace. Thearray includes a matrix of W*L number of spot IR sources, each of whichcovers a fixed area. The On/Off behavior of the spot IR sources may beindividually controlled by a computer so that each spot on the edge willbe illuminated by the IR sources for a pre-determined fixed totalenergy, e.g., equal to the amount required to melt the frit. The widthof the array may cover the whole effective width of the belt, and thelength of the array may provide sufficient heating to melt the frit. Thelength of the array can be estimated by the equation:E=L*D/Vwhere E is the total energy per unit area used in melting the frit, L isthe length of the array, D is the power density of the IR source, and Vis the furnace line speed.

The operation of the array of IR sources will now be described ingreater detail with reference to FIGS. 9a-9f . For convenience, theindividual heat sources will be identified using a naming scheme whereeach individual source is designated as #LW, with the L- and W-axesbeing numbered as “1” at the intersection thereof shown in FIG. 9a .Thus, for example, in FIGS. 9a-9f , the upper-left heat source is #98,and the bottom-right heat source is #11.

FIG. 9a is an overhead view of the VIG assembly 1′ on a belt 92 in anoven prior to its entry under the IR source array 90, in accordance withan example embodiment. Before the VIG assembly 1′ goes under the IRsource array 90, all IR sources are turned off (e.g., as designated byall circles in the IR source array 90 being greyed-out).

FIG. 9b is an overhead view of the VIG assembly 1′ on a belt 92 in anoven entering into the IR source array 90, in accordance with an exampleembodiment. When the leading edge of the VIG assembly 1′ is under thearray, the IR sources covering the edge of the VIG assembly 1′ to besealed are turned on. Thus, in the FIG. 9b example, units #11 to #16 areturned on, as designated by the darkened circles. At this time, theother sources in the IR source array 90 remain off.

FIG. 9c is an overhead view of the VIG assembly 1′ further entering theIR source array 90 such that both the edge to be sealed along the minoraxis of the VIG assembly 1′ and portions of the edges to be sealed alongthe major axis of the VIG assembly 1′ are both exposed to IR from the IRsource array 90, in accordance with an example embodiment. As shown inFIG. 9c , the VIG assembly 1′ further enters the array region, and theIR sources switch from W=1 to W=2 and then to W=3 to follow the leadingedge. In the mean time, #11, #21, #16 and #26 remain “on” because theedges to be sealed along the major axis of the VIG assembly 1′ are to beexposed to heat.

FIG. 9d is an overview of the VIG assembly 1′ further entering the IRsource array 90 such that only the edges to be sealed along the majoraxis of the VIG assembly 1′ are exposed to IR from the IR source array90, in accordance with an example embodiment. Once only the side edgesare under the array, the “On” pattern becomes two parallel lines in themoving direction, and all other heat sources are turned “Off.” As shownin FIG. 9d , a second VIG assembly 1′ having edges to be sealed iscoming down the belt 92 towards the array.

FIG. 9e is an overhead view of the VIG assembly 1′ exiting the IR sourcearray 90, in accordance with an example embodiment. As the trailing edgeenters the array, the column L=1, 2, 3, . . . , will be turned on againin this order for the trailing edge. The whole column will be completelyoff after the trailing edge passes until the next assembly 1′ enters. Bythe time the VIG assembly 1′ leaves the array region 90, every spot onthe perimeter has received a substantially equal amount of energysufficient to melt the frit.

FIG. 9f is an overhead view of a second VIG assembly 1′ entering the IRsource array 90 as a first VIG assembly 1′ exits the IR source array 90in accordance with an example embodiment. As can be seen from FIG. 9f ,the first and second VIG assemblies 1′ are differently sized. Thus, whenthe second VIG assembly 1′ enters the array region, the process willrepeat, except that row W=7 will be on because of larger width for thesecond unit.

Thus, it will be appreciated that each heat source in each row andcolumn of the array is selectively activated in dependence on whether anedge to be sealed is proximate to the heat source (e.g., within an areaof heat produced by the heat source). It also will be appreciated thatthe array is substantially two-dimensional.

The determination of which sources to be turned on may be pre-programmedby an operator in certain example embodiments. In certain exampleembodiments, photo-eye or other detecting mechanisms may be used todetermine the size and/or position of the VIG assembly, e.g., todetermine the heat sources in the array to be turned on and the time atwhich they should be turned on.

It will be appreciated that the energy intensity produced by a single IRheat source (e.g., in an array) is substantially normally distributedacross an area such that the energy emitted is highest at the center ofthe area. Thus, an arrangement that incorporates an array ofspaced-apart IR heat sources may sometimes create “stripes” of high andlow energy areas. Sometimes, this may result in localized andnon-localized melting. That is, sometimes just enough or too much energywill be applied to a certain area or areas, while not enough energy willbe provided to an adjacent area or areas.

Accordingly, certain example embodiments may incorporate an array of IRheat sources where the heat sources are staggered. FIG. 10 is anoverhead view of an IR source array 90′ incorporating a staggered IRheat source design, in accordance with an example embodiment. In FIG.10, the individual heat sources in the array 90′ are arranged such that,moving left-to-right, the southeast section of the first heat source isadjacent to the northwest section of the second heat source, and thenortheast section of the second heat source is adjacent to the southwestsection of the third heat source, etc. This and/or other arrangementsmay advantageously help provide alternating high and low exposure areasto even out the striping that sometimes may otherwise occur. Thestaggered IR heat source design of FIG. 10 operates in substantially thesame was as the design of FIGS. 9a -9 f.

In certain example embodiments, diffusers may be placed proximate toeach lamp so as to even out the energy, which otherwise sometimes mightbe provided according to a particular shape (e.g., circular shape wherecircular lamps are used) or in stripes as noted above, thus providing asubstantially uniform distribution of heat across the area to be heated.Generally, a diffuser may be provided to each heat source in the arrayto provide a more uniform heat flux from the heat sources in the array.It will be appreciated that diffusers may be used in connection witheither the array design of FIGS. 9a-9f and/or the array design of FIG.10.

FIG. 11a is a side view of an in-line style belt furnace installed withan array 90 of IR sources. Pre-assembled VIG assemblies 1′ enter thefurnace and are heated up through a temperature ramp-up zone to reachthe predetermined background temperature (typically between about200-300° C.). An IR array 90 is installed in this background temperaturezone and melts the frit around the perimeter of the VIG assemblies 1′ ina process described above or other process. During the whole time, thefurnace belt 92 may be moving continuously at a constant speed selectedto provide sufficient heating to the perimeters of the VIG assemblies 1′to ensure good hermetic seals around the edges of the VIG assemblies 1′.The pumping port tube seal, if necessary, can also be sealed in the sameor other fashion using the IR array 90 at the same time. The individualIR heat sources are switched on and off by computer-control to provideadequate preferential heating to the edges of the VIG assemblies 1′. Thetemperature of the frit on the edge of the VIG assemblies 1′ iscontrolled between about 350-500° C., suitable to melt frit but belowglass melting point. In the meantime, the glass temperature remains ator close to the background temperature. The VIG assembly 1′ is thentransported through temperature ramp down zones until it cools down,e.g., to less than about 100° C. when it exits the oven. As noted above,the zones may be separate chambers or they may be the same chambers incertain example embodiments.

It will be appreciated that when turning on a single IR heat source, theenergy produced is substantially normally distributed over time. Thus,the energy will often ramp-up, stabilize, and then ramp-down.Accordingly, in certain example embodiments, a computer-controlledsystem may advantageously turn on a single lamp before the VIG assemblyis underneath it to ensure that the intended energy reaches the area,and/or also turn off the lamp before the VIG assembly exits to reducethe exposure to adjacent areas that should not be heated. Thus, as theunit moves across successive columns of the array, each heat source isactivated in the row and column of the array before the edge to besealed is exposed to heat emanating from the heat source and alsodeactivated before the edge to be sealed is removed from the heatemanating from the heat source.

FIG. 11b is a side view of an in-line style belt furnace installed withtwo arrays 90 of IR sources in accordance with an example embodiment.For example, an additional array may be provided between the belt andpoint upward so that the two arrays heat the edges to be sealed fromboth sides. That is, heat may be applied to both sides of the frit toensure faster and/or more uniform melting thereof. The two arrays 90 maybe controlled in the same way by the same or different means to ensurethat the edges become sealed. Alternatively, a slight delay betweenon-off cycles or slightly different on-off configuration may beintroduced between arrays, e.g., to help reduce the striping problemdescribed above.

It will be appreciated that the example embodiments described herein maybe used in connection with a variety of different VIG assembly and/orother units or components. For example, the substrates may be glasssubstrates, heat strengthened substrates, tempered substrates, etc.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method of making a vacuum insulating glass(VIG) unit, the method comprising: having first and second substantiallyparallel spaced-apart thermally tempered glass substrates and an edgeseal material comprising frit provided at least partially between thefirst and second thermally tempered glass substrates for sealing an areaproximate an edge of the VIG window unit; providing localized nearinfrared (IR) inclusive heat from about 1.1 to 1.4 μm proximate to anarea proximate the edge to be sealed via a two-dimensional array of heatsources so as to at least partially melt the frit, and wherein the heatsources are individually and selectively activated, in sequence; coolingthe frit and/or allowing the frit to harden in making the vacuuminsulating glass (VIG) unit; wherein at least some portions of the firstand second glass substrates do not lose any more than 50% of originaltemper strength during formation of the edge seal; and evacuating a gapbetween the first and second thermally tempered glass substrates to apressure less than atmospheric pressure in making the vacuum insulatingglass (VIG) unit.
 2. The method of claim 1, further comprising providinga plurality of spacers between the glass substrates for spacing theglass substrates apart.
 3. A method of making a vacuum insulating glass(VIG) unit, the method comprising: having first and second substantiallyparallel spaced-apart glass substrates and an edge seal materialprovided at least partially between the first and second glasssubstrates for sealing an area proximate an edge of the VIG unit;pre-heating the glass substrates and the edge seal material to at leastone temperature from about 200 to 300 degrees C. which is below amelting point of the first and second glass substrates and below amelting point of the edge seal material; providing localized nearinfrared (IR) inclusive heat from about 1.1 to 1.4 μm proximate to thearea proximate the edge to be sealed via a two-dimensional array of heatsources so as to at least partially melt the edge seal material, andwherein the heat sources are individually and selectively activated, insequence; cooling the edge seal material and/or allowing the edge sealmaterial to harden in making the vacuum insulating glass (VIG) unit; andevacuating a gap between the first and second glass substrates to apressure less than atmospheric pressure in making the vacuum insulatingglass (VIG) window unit.
 4. The method of claim 3, further comprisingproviding a plurality of spacers between the glass substrates forspacing the glass substrates apart.
 5. The method of claim 1, whereinthe heat sources are arranged in a plurality of rows and/or columns. 6.The method of claim 5, wherein the heat sources in adjacent rows and/orcolumns are staggered.
 7. The method of claim 1, wherein the heatsources comprise spot IR sources.